Traffic reports on the radio or television provide useful information to travelers about accidents, heavy traffic, construction, and other conditions which can cause increases in expected travel times. This information is broadcast periodically, but may not be readily available when a person actually needs a report. Additionally, such reports only cover major highways and commuting routes. Often, drivers experience significant delays on routes which are not reported in any traffic reports. Therefore, it would be useful for drivers to be able to obtain accurate traffic reports covering the roads they intend to travel.
In addition to difficulties in providing useful reports, news agencies have difficulty in acquiring relevant traffic information for the roads which they do cover. Often, traffic report information is based upon personal observations provided to a news agency. News agencies have been using helicopters in order to monitor the major highways for significant backups and delays. They also use information provided to them from actual drivers as to delays, traffic conditions and travel times. Such sources cannot provide particularly useful information or objective data as to the likely extent of delays in traffic.
Various attempts have been made to create automated systems for determining traffic information, and to provide more objective estimates of traffic flow. For example, U.S. Pat. No. 5,465,289 discloses a method and apparatus for determining vehicular traffic information using existing cellular telephone technology. Sensors are used to monitor cellular telephone communication information. Data from the cellular communications are extracted and analyzed to determine vehicle locations and travel information. The system requires a statistical model for determining location of automobiles within each cell of the cellular system. As with news reports, this system only provides information relating to major thoroughfares, and cannot provide information relating to individual street segments.
In addition to traffic report information, systems have been and are being developed for providing route planning information and navigational assistance to drivers. One such system is illustrated in U.S. Pat. No. 5,272,638, assigned to Texas Instruments Incorporated. This system includes a digital road map database providing information about road segments, intersections, and travel times for road segments. Information in the database is used to plan routes having minimal travel time from one location to another. More efficient route planning is obtained by using a route hierarchy of local areas around the starting and ending locations, major thoroughfares between local areas, and major freeways for longer travel distances. Preferably, vehicle location information can be determined using satellite systems or some other positioning method. Instructions can then be provided audibly or visually to the driver when turns are necessary in the travel plan. This patent provides suggestions for a process for determining a route based upon the travel destination and the travel times stored in the database. However, the patent does not describe how the information in the database can be obtained. It suggests that dynamic traffic information can be obtained through a traffic interface. A traffic interface may receive digital broadcast over radio sidebands, or from centralized cellular phone systems containing information on traffic obstacles such as accidents and amounts of the resulting delays. However, no suggestion is made as to how such dynamic information is collected or organized for transfer to the system in the vehicle. Therefore, a need exists for a system which provides for collection, organization and dissemination of traffic information which can be used in a route planning and navigation system.
U.S. Pat. No. 5,459,667, assigned to Sumitomo Electric Industries, Ltd., is another example of a vehicle navigation system. The system disclosed in this patent provides for more accurate vehicle location determinations and a capability to determine whether the vehicle is traveling on an optimum route between starting and ending locations. As with the previously-described system, this system uses a database having information relating to street segments and travel times in order to estimate the optimum route. Preferably, the travel information is stored in a CD ROM. Since the information is stored in a CD ROM, it is not easily changeable and cannot be adjusted for changes in travel times resulting from changes in road conditions. Again, this system does not determine how to create the database, to determine travel time, or how to adjust travel time to account for traffic conditions.
The Illinois Department of Transportation is developing a system, called ADVANCE (Advanced Driver and Vehicle Advisory Navigation ConcEpt). The ADVANCE system is described in several articles including "Operation of the ADVANCE Traffic Information Center" by Jeffrey Hochmuth (Jan. 25, 1995) and "ADVANCE-Initial Deployment" by Joseph S. Ligas and Syde Bowott, ITS America, 1995 Annual Conference (March, 1995). A traffic information center collects and organizes traffic data from a variety of sources. These sources include a closed loop traffic signal system, a cellular based motorist call-in system, a motorist assistance system, and emergency dispatch systems. The information is used to create historical databases and a CD ROM of travel data. Each vehicle is provided with a mobile navigation assistant, which provides route planning using both static and dynamic travel time data. Static data are provided by the CD ROM. The mobile navigation system provides route planning and navigational information similar to the systems described above. In addition to static information, the mobile navigation assistance communicates with the traffic information center through a radio frequency communications network to obtain dynamic traffic information data. The dynamic traffic data can be used for more accurate route planning, or for rerouting based upon new information. The ADVANCE system also anticipates using vehicles as traffic probes to provide real time traffic information. The vehicles would transmit data to the traffic information center over the radio frequency communications network on recently traversed streets in the system. The traffic information center would combine this information with the traffic information from other sources in creating its dynamic traffic data. Although the ADVANCE system is still being developed and the descriptions are incomplete, several disadvantages are apparent in the system. Significant additional equipment is needed in the vehicle to operate the system. Much of this equipment is duplicative of functions performed by other equipment already present in many vehicles. The radio communications equipment would need specific frequencies and may interfere with other radio communications. Additionally, no method for combining dynamic data from automobiles with other information relating to potential traffic delays is indicated. The use of additional information may cause distortion of the dynamic traffic data unless the effect of the traffic conditions from the outside sources can be accurately reflected in the travel times used for route planning.
Furthermore, each of the navigation systems described above include only travel times for various street segments. Often, delays are caused by transitions between street segments.